1. Field of the Invention
The present invention relates to a structure and method for connecting a terminal and an electric wire, in which a wire connecting portion of the terminal can uniformly be press-connected to a core wire portion of the electric wire, reliable electric contact of the connected portion thereof is obtained, and an interlocking force thereof is improved.
The present application is based on Japanese Patent Applications Nos. 2000-286954, 2000-317982 and 2001-256720, which are incorporated herein by reference.
2. Description of the Related Art
According to a mode of a structure for connecting an electric wire to a terminal, as shown in FIG. 1, a core wire portion 45 at a peeled terminal end of an electric wire 44 is clamped by a pair of crimping pieces 42 which are provided on both sides of a bottom plate portion of a terminal 41 in such a manner as to erect therefrom for fixed press attachment, so that a contact between the core wire portion 45 and the crimping pieces 42 is obtained.
The terminal 41 has a circular plate-like electric contact portion 46 at one end, the pair of core wire crimping pieces 42 as an wire connecting portion at the other end thereof and a pair of coating crimping pieces 43 provided rearward of the pair of the core wire crimping pieces. The coating crimping pieces 43 are press attached fixedly to an insulating resin coating of the electric wire 44, whereby the core wire portion 45 is prevented from being dislocated from the core wire crimping pieces 42.
According to a crimping method shown in FIG. 2, the pair of crimping pieces 42 are crimped in a eyeglasses-like manner between an upper crimper 47 and a lower anvil 48 and respective strands of the core wire portion 45 are compressed between the pair of crimping pieces 42 and a bottom plate portion 49.
However, while the connecting structure using the aforesaid solderless or crimping terminal 41 is effective for electric wires 44 of small diameters, for the electric wires of large diameters such as shield electric wires for conducting large current the connecting structure causes a problem that the contact area between the crimping pieces 42 and the core wire portion 45 becomes smaller, increasing electric resistance. In addition, since the crimping pieces 42 are strongly bent from the bottom plate portion 49 in the vicinity of where the crimper 47 is in contact with the anvil 48, the connecting structure also causes a problem that stress concentrates in bent portions, and the mechanical strength of the terminal 41 is lowered depending upon ways in which the crimping pieces 42 are bent.
To cope with this, there has been used a terminal 51 of a type in which a core wire connecting portion is crimped circumferentially at equal intervals, as shown in FIG. 3. This terminal 51 has a cylindrical electric contact portion 52 at one end and a cylindrical wire connecting portion 53 at the other end thereof, and the wire connecting portion 53 is crimped circumferentially at equal intervals into, for example, a hexagonal shape with a peeled core wire portion at a terminal end of an electric wire 54 being inserted into the wire connecting portion 53. A coated portion 55 of the electric wire 44 is located rearward of the wire connecting portion 53 with a gap being provided therebetween. A mating male connector (not shown) is connected to the electric contact portion 52 located on the front side of the terminal 51 by inserting or screwing the former into the latter.
An embodiment of a connecting method (a connecting structure) of this type for connecting the terminal 51 and the electric wire 44 has been recited in Examined Japanese Utility Model Publication No. Sho. 50-43746, and will be described below with reference to FIG.
In this connecting method, an wire connecting portion 62, initially formed into a cylindrical shape, is crimped into a hexagonal shape with a pair of upper and lower die halves 63 with a core wire portion 61 of the electric wire being inserted into the cylindrical wire connecting portion of the terminal so that the core wire portion 61 is caused to adhere to the wire connecting portion 62 from inside as well as to each other. In each die half 63, as shown in FIG. 5, there are formed three pressing surfaces 64, and an elongate projection 65 is formed on each pressing surface 64. As shown in FIG. 4, the elongate projections 65 press against central portions of external surfaces of the hexagonal wire connecting portion 62, respectively, in radial directions so that the contact qualities of the core wire portion 61 of the electric wire and the wire connecting portion 62 of the terminal are improved.
However, in the aforesaid connecting method and a connecting structure using the same method, as shown in FIG. 4, burrs 60 tend to be generated on both sides of the wire connecting portion between the upper and lower die halves 63, and this causes a problem that many man-hours are disadvantageously required to remove the burrs 60 so generated. More over, when the wire connecting portion 62 of the terminal is crimped with the pair of upper and lower die halves 63, as shown in FIG. 6, a crimping force (internal stress) P1 directed toward the center of the core wire portion 61 tends to act largely, whereas crimping forces (internal stresses) P2 applied to both sides of the core wire portion 61 tend to be reduced, and this tends to cause a problem that gaps are produced between strands of the core wire portion 61, as well as between the core wire portion 61 and the wire connecting portion 62 on both the sides of the wire connecting portion 62 of the terminal. In case such gaps are produced, electric resistance is increased, and energizing efficiency is reduced. Moreover, there is caused a concern that the connecting portion is heated.
In addition, in a case where aluminum material is used for the core wire portion 61, since an oxidized coating on the surface of the core wire portion 61 is thick, the coating needs to be broken, but the oxidized coating cannot be completely removed when the core wire portion 61 is clamped by the pair of crimping pieces 42 for connection or when the cylindrical wire connecting portion 53 is crimped into the hexagonal shape for connection, whereby there is also caused a problem that the electric resistance is increased, and the reliable electric connection is damaged.
In addition, FIG. 7 shows the result of crimping an electric wire for connection using a similar method to that illustrated in FIG. 4. Since elongate projections 65 formed on die halves 63 press against a core wire portion 61xe2x80x2 at six positions thereon in radial directions as indicated by arrows F, the core wire portion 61xe2x80x2 is deformed into a turtle-like shape in cross section, and stress concentration (chain lines 79 indicate an internal stress distribution) occurs in an wire connecting portion 62xe2x80x2 of a terminal between respective recessed portions 77 produced by the respective elongate projections 65 (FIG. 5), or at raised portions 78, whereby the core wire portion 61xe2x80x2 cannot be circumferentially uniformly crimped. This helps form easily gaps 70 in the interior of the core wire portion 61xe2x80x2 (gaps between respective strands), as well as gaps 70 between the core wire portion 61xe2x80x2 and the wire connecting portion 62xe2x80x2 of the terminal, and cracks are also easily generated in the wire connecting portion 62xe2x80x2 due to the stress concentration. Thus, there is caused a problem that the mechanical strength of the wire connecting portion is deteriorated. In case there are formed gaps 70, 71, as with the previous case, electric resistance is increased, thereby decreasing energizing efficiency. In addition, there are caused concerns that the wire connecting portion 62xe2x80x2 is heated and that the core wire portion 61xe2x80x2 is easily dislocated from the wire connecting portion 62xe2x80x2.
Furthermore, in the structure for connecting the terminal 51 and the electric wire 54 shown in FIG. 3, since the respective strands of the core wire portion of the electric wire 54 line contact the inner circumferential surface of the wire connecting portion 53 of the terminal 51 in the longitudinal direction, the mechanical strength is weak against crimping, and therefore, in case a strong tensile force acts on, for example, the electric wire 54 or the terminal 51, there is caused a concern that the core wire portion tends to be dislocated from the wire connecting portion 53.
The present invention was made in view of the aforesaid situations, and an object thereof is to provide a structure for connecting a terminal and an electric wire which can ensure, of course, that the core wire portion of the electric wire and the wire connecting portion of the terminal, as well as the respective strands of the core wire portion are brought into contact without any gap being produced therebetween, additionally, that even if the core wire portion is used which has the thick oxidized coating resulting when the aluminum material is used, the core wire portion is brought into contact with the wire connecting portion of the terminal with low electric resistance, and moreover, that even in case the strong tensile force acts on the electric wire or the terminal, the core wire portion is not dislocated from the wire connecting portion.
Further, another object thereof is to provide a method and structure for connecting a terminal with an electric wire in which the cylindrical wire connecting portion of the terminal can be circumferentially uniformly crimped around the electric wire such that there is caused no scattering of internal stress and beautifully such that there is caused no burrs, whereby there is caused no gap between the strands in the core wire portion of the electric wire and between the core wire portion and the wire connecting portion of the terminal, thereby improving the reliability in electrically connecting the electric wire with the terminal and improving the mechanical strength of the wire connecting portion of the terminal.
To achieve the above objects, according to a first aspect of the present invention, there is provided a structure for connecting a terminal and an electric wire. The structure comprises a tubular wire connecting portion, into which a core wire portion of an electric wire is insertable, formed on a terminal, and a core wire engagement portion formed in a circumferential wall of the wire connecting portion, the core wire engagement portion intersecting with an internal surface of the circumferential wall, wherein the wire connecting portion is crimped around a full outer circumference thereof in a state in which the core wire portion of the electric wire is inserted into the wire connecting portion, whereby the core wire portion at least partially enters an interior of the core wire engagement portion and is engaged with the core wire engagement portion.
According to a second aspect of the present invention, it is effective that the core wire engagement portion includes a hole portion formed through the circumferential wall of the wire connecting portion, or a groove portion.
According to a third aspect of the present invention, it is also effective that a plurality of the core wire engagement portions are disposed circumferentially in the wire connecting portion.
According to a fourth aspect of the present invention, it is also effective that an intersecting portion, at which the core wire engagement portion intersects with the internal surface of the circumferential wall, is formed into an edge.
According to a fifth aspect of the present invention, there is provided a structure for connecting a terminal and an electric wire. The structure comprises a tubular wire connecting portion, into which a core wire portion of an electric wire is insertable, formed on a terminal, and a plurality of irregularities formed on an internal circumferential surface of the wire connecting portion of the terminal, wherein the wire connecting portion is crimped around a full outer circumference thereof in a state in which the core wire portion of the electric wire is inserted into the wire connecting portion, whereby the irregularities bite into the core wire portion of the electric wire.
According to a sixth aspect of the present invention, it is effective that the irregularities include at least one spiral groove and a plurality of thread portions.
According to a seventh aspect of the present invention, it is also effective that the core wire portion of the electric wire is twisted, and wherein a spiral direction of the irregularities is opposite to a twisting direction of the core wire portion of the electric wire.
According to an eighth aspect of the present invention, it is also effective that the irregularities include groove portions and thread portions, and wherein the groove portions and thread portions intersect with each other.
According to a ninth aspect of the present invention, there is provided a method for connecting a terminal to an electric wire. The method comprises the steps of:
providing a terminal including a tubular wire connecting portion;
inserting a core wire portion of an electric wire into the wire connecting portion of the terminal;
crimping the wire connecting portion in a radial direction of the electric wire; and
uniformly compressing the wire connecting portion around a full outer circumference thereof in the radial direction of the electric wire.
According to a tenth aspect of the present invention, it is effective that, in the uniformly compressing step, while a die is rotated using a rotary swaging device, the wire connecting portion of the terminal is compressed with the die.
According to an eleventh aspect of the present invention, it is effective that the method of the tenth aspect further comprises forming a projecting portion on an outer circumference of the wire connecting portion, wherein, in the uniformly compressing step, the projecting portion is pressed, thereby causing an inner surface of the wire connecting portion to partially inwardly project so as to bite into the core wire portion.
According to a twelfth aspect of the present invention, there is provided a structure for connecting a terminal to an electric wire. The structure comprises a tubular wire connecting portion, into which a core wire portion of an electric wire is insertable, formed on a terminal, the wire connecting portion being crimped in a radial direction of the electric wire, wherein the wire connecting portion is uniformly compressed along a full outer circumference thereof in the radial direction of the electric wire, whereby a circumference of a compressed portion of the wire connecting portion is formed into a round shape in cross section.
According to a thirteenth aspect of the present invention, it is preferable that the structure of the twelfth aspect further comprises a projecting portion formed on an outer circumference of the wire connecting portion before the wire connecting portion is crimped, wherein the projecting portion is pressed when the wire connecting portion is uniformly compressed, thereby causing an inner surface of the wire connecting portion to partially inwardly project so as to bite into the core wire portion.
According to a fourteenth aspect of the present invention, the projecting portion may include a circumferentially elongated projection or at least one projection.